Optimization of a Luciferase-Expressing Non-Invasive Intrapleural Model of Malignant Mesothelioma in Immunocompetent Mice

Our plain-English summary of Optimization of a Luciferase-Expressing Non-Invasive Intrapleural Model of Malignant Mesothelioma in Immunocompetent Mice, by E. Digifico, M. Erreni, F.S. Colombo, et al (Cancers, 2020).

The study

• Authors: E. Digifico, M. Erreni, F.S. Colombo, C. Recordati, R. Migliore, R. Frapolli, M. D'Incalci, C. Belgiovine, P. Allavena
• Journal: Cancers
• Published: 2020;12(8)
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant Pleural Mesothelioma (MPM) is an aggressive tumor of the pleural lining that is usually identified at advanced stages and resistant to current therapies. Appropriate pre-clinical mouse tumor models are of pivotal importance to study its biology. Usually, tumor cells have been injected intraperitoneally or subcutaneously. Using three available murine mesothelioma cell lines with different histotypes (sarcomatoid, biphasic, epithelioid), we have set up a simplified model of in vivo growth orthotopically by inoculating tumor cells directly in the thorax with a minimally invasive procedure. Mesothelioma tumors grew along the pleura and spread on the superficial areas of the lungs, but no masses were found outside the thoracic cavity. As observed in human MPM, tumors were highly infiltrated by macrophages and T cells. The luciferase-expressing cells can be visualized in vivo by bioluminescent optical imaging to precisely quantify tumor growth over time. Notably, the bioluminescence signal detected in vivo correctly matched the tumor burden quantified with classical histology. In contrast, the subcutaneous or intraperitoneal growth of these mesothelioma cells was considered either non-representative of the human disease or unreliable to precisely quantify tumor load. Our non-invasive in vivo model of mesothelioma is simple and reproducible, and it reliably recapitulates the human disease.

In plain English

This was a laboratory animal study in which the authors set up and characterised an orthotopic (intrapleural) mouse model of malignant pleural mesothelioma. Three murine mesothelioma cell lines previously generated in BALB/c mice after intraperitoneal injection of crocidolite asbestos fibres were used: AB1 (sarcomatoid), AB12 (biphasic) and AB22 (epithelioid), all expressing luciferase. Cells were injected subcutaneously or intraperitoneally (1 x 10^5) or directly into the thorax between the third and fourth costal space (5 x 10^4). After intrathoracic injection of 50 mice, engraftment was 100% and tumour growth developed in 94%, with 3/50 mice having very slow growing tumours. Tumours grew on the pleura and lung surfaces, and no masses were found outside the thoracic cavity. The bioluminescence signal generally increased over time, although the AB1 growth curve bent around day 11 before rising again. The signal correlated closely with tumour area measured by histology. Tumours were infiltrated by IBA1+ macrophages, while CD3+ lymphocytes were rare. The authors concluded that their intrathoracic model is simple, reproducible and recapitulates the growth pattern of human MPM.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: animal experiment in immunocompetent mice (orthotopic tumour cell transplantation model, with comparison of subcutaneous and intraperitoneal injection)
• Who was studied: BALB/c mice, 8 weeks old, injected with three murine mesothelioma cell lines (AB1, AB12, AB22). 50 mice received intrathoracic injection. Smaller groups received subcutaneous injection (AB1 n = 8, AB12 n = 5, AB22 n = 3) or intraperitoneal injection (AB1 n = 7, AB12 n = 5). The work was carried out in Italy and published in 2020.
• Exposure: Injection of luciferase-expressing murine mesothelioma cells (AB1 sarcomatoid, AB12 biphasic, AB22 epithelioid). These cells were originally derived from BALB/c mice given intraperitoneal crocidolite asbestos fibres. Doses were 5 x 10^4 cells intrathoracically, or 1 x 10^5 cells subcutaneously or intraperitoneally.
• Main results:
  • Intrathoracic injection: engraftment in 100% of 50 mice and tumour growth over time in 94%. 3/50 mice had detectable but very slow growing tumours.
  • After intrathoracic injection, tumours stayed within the chest, growing on the pleura and infiltrating the lung lobes
  • Timing of detectable intrathoracic growth differed by histotype: AB1 (sarcomatoid) from day 4 to 6, AB12 (biphasic) from day 7, AB22 (epithelioid) after day 9
  • The intrathoracic bioluminescence signal increased over time, but the AB1 growth curve bent around day 11 after injection and then grew again at later times
  • Bioluminescence measured in vivo corresponded closely to tumour area on histology. The text gives 25 mice; the figure legend gives n = 26 mice.
  • In the intrathoracic tumours of all three cell lines, macrophages and vessels were abundant while T lymphocytes were very rare. AB22 tumours had more neutrophils.
  • In subcutaneous tumours, AB1 and AB22 tumours were dominated by myeloid cells (up to 70-80% of CD11b+ cells out of total CD45+ cells). AB12 tumours had similar myeloid and lymphoid infiltration.
  • In the intraperitoneal model with AB1 cells, luciferase signal was seen in 3/5 mice at day 6 and 4/5 at day 14, and did not increase linearly. At autopsy one mouse had an intestinal block and two had extensive haemorrhagic areas.
• The authors' conclusion: The authors concluded that their minimally invasive intrathoracic model is simple and reproducible, gives linear bioluminescent quantification matching histology, and faithfully recapitulates the growth pattern of human malignant pleural mesothelioma
• Limitations the authors state:
  • The authors noted that in the intraperitoneal model some mice died from severe involvement of vital organs rather than from large tumour masses
  • The authors noted that in the intraperitoneal model the many small tumour masses were difficult to collect for a precise quantification of tumour burden
  • The authors offered the bending of the AB1 growth curve around day 11 only as a likely explanation, not a demonstrated one

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Pleural Mesothelioma, Sarcomatoid, Biphasic Mesothelioma, Epithelioid, Thorax, Pleura, Macrophage.

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• Quantitative structure-mesothelioma potency model optimization for complex mixtures of elongated particles in rat pleura: A retrospective study — P.M. Cook, J. Swintek, et al. (2016)
• Development of lung tumors in mutant p53-expressing mice after inhalation exposure to asbestos — G.F. Morris, A.R. Notwick, et al. (2004)

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